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1
Heat the oven to 375F or 350F on convection.
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2
Line a baking sheet with a Silpat or parchment.
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3
Cut the butter into pieces and put it in the bowl of a standing mixer fitted with the paddle.
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4
Whisk the cocoa powder, flour, sugar, and salt together and add to the bowl.
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5
Mix at medium speed until well combined, dark brown, and in big crumbs.
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6
Spread out on the baking sheet, breaking up the biggest crumbs and leaving room for spreading.
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7
Bake until crisp, about 20 minutes, rotating the pan halfway through baking.
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8
Let cool.
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9
When the crumble is cool, put it in a food processor and process to fine, even crumbs.
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10
Store in an airtight container for up to 1 week.
